This invention relates to a method of preparing poly(arylene ether ketones) and in particular to an electrophilic dispersion polymerization process for preparing such polymers.
Poly(arylenes), in particular all para-linked poly(arylene ether ketones), possess many desirable properties, for example, high temperature stability, mechanical strength, and resistance towards common solvents. This invention is directed to an improved electrophilic synthesis for preparing poly(arylenes), in particular all para-linked poly(arylene ether ketones).
In an electrophilic synthesis, the polymerization step involves the formation of an aryl ketone group from a carboxylic acid or acid derivative group and an aromatic compound containing an aromatic carbon bearing an activated hydrogen atom, i.e., a hydrogen atom displaceable under the electrophilic reaction conditions. The monomer system employed in the polymerization can be, for example, (a) a single aromatic compound containing both an acid or acid derivative group as well as an activated hydrogen atom on an aromatic carbon for example, p-phenoxybenzoyl chloride; or (b) a two component system of a dicarboxylic acid or acid derivative and an aromatic compound containing two activated hydrogen atoms, for example, terephthaloyl chloride and 1,4-diphenoxybenzene.
Electrophilic polymerization of this type is often referred to as Friedel-Crafts polymerization. Typically, such polymerizations are carried out in a reaction medium comprising the reactant(s), a catalyst, such as anhydrous aluminum trichloride, and solvent such as methylene chloride, carbon disulfide, nitromethane, nitrobenzene, or ortho-dichlorobenzene. Because the carbonyl groups of the reactant(s) and products complex with aluminum trichloride and thereby deactivate it, the aluminum trichloride catalyst is generally employed in an amount greater than one equivalent for each equivalent of carbonyl groups in the reaction medium. Other inorganic halides such as ferric chloride, may be employed as the catalyst. Since ferric chloride does not complex with carbonyl groups less than molar amounts may be used.
Such Friedel-Crafts polymerizations generally have produced an intractable reaction product difficult to remove from the reaction vessel and purify. Further, such processes have tended to produce polymer of undesirably low molecular weight and/or of poor thermal stability. The all para-linked poly(arylene ether ketones) have been particularly difficult to prepare under such Friedel-Crafts conditions. Typically, when a monomer or mixture of monomers is added to a suspension of the Lewis acid catalyst in a suitable diluent, the initially formed catalyst/monomer complex is soluble but as the polymerization proceeds, phase separation of the growing polymer chains and/or their complex with the Lewis acid catalyst occurs and the walls and floors of the reaction vessel becomes covered with a hard gel which becomes harder and more intractable as the reaction continues.
One factor that appears to contribute to the unsatisfactory results reported in the literature is that the para-linked polymers are more highly crystalline than the ortho, meta or mixed isomeric members of this polymer family and are therefore generally more insoluble in the reaction media typically used in such Friedel-Crafts reactions. This tends to result in the premature precipitation of the polymer in a form in which further polymerization does not occur. Another factor that may lead to these poor results is deactivation of the terminal aryloxy groups by complexation with aluminum chloride or alkylation of the terminal group which prevents further growth of the polymer chain. Also, side reactions, particularly at the ortho position of activated aromatic rings can result in a polymer that is branched and/or is more likely to cross-link at elevated temperatures such as those required for melt processing the polymer. It is generally recognized that in Friedel-Crafts reactions, ortho substitution of the polymer is more likely to occur if the reaction is conducted at elevated temperatures and/or for a relatively long reaction time. U.S. Pat. Nos. 3,065,205 to Bonner, 3,767,620 to Angelo et al, 3,516,966 to Berr, 3,791,890 to Gander et al, 4,008,203 to Jones and U.K. Pat. Nos. 971,227 and 1,086,021 both to Imperial Chemical Industries, Limited, disclose the preparation of poly(arylene ketones) by Friedel-Crafts polymerization and generally acknowledge some of the difficulties in producing tractable, melt stable polymers. For example, Gander et al provide a method of producing the polymers in granular form by special treatment of the reaction mixture before gellation can occur and Angelo et al provide the method of treating the polymer to reduce undesired end groups which result from side reactions during polymerization and which cause thermal instability of the polymer.
To overcome the disadvantages encountered in producing poly(arylene ketones) by the above described Friedel-Crafts polymerization, it has been proposed to use boron trifluoride catalyst in anhydrous hydrogen fluoride. See for example, U.S. Pat. Nos. 3,441,538 to Marks, 3,442,857 to Thornton, 3,953,400 to Dahl, and 3,956,240 to Dahl et al. This general process has been used commercially to produce polymer of the desired high molecular weight and thermal stability by solution polymerization. However, the use of boron trifluoride and hydrogen fluoride requires special techniques and equipment making this process difficult to practice on a commercial scale.
In the earlier copending commonly assigned application Ser. No. 594,503, is described a method of preparing poly(arylene ketones) under controlled or moderated conditions using a controlling agent or specified amounts of Lewis acid catalyst, depending on the monomer system employed. The controlling agent generally maintains the polymer in solution or in a swollen gel form in which polymerization to high molecular weight polymer could take place. Certain of the controlling agents described in this previous application have been discovered to be effective dispersants for the polymerization process. Further, effecting the polymerization, with or without a dispersant, under conditions which maintain the polymer and/or its complex with the Lewis acid catalyst suspended in the reaction medium, provides an additional method of producing substantially linear, high molecular weight polymer. Since the process of this invention maintains the polymer in suspension in finely divided particulate form, recovery and purification of the polymer is greatly facilitated.